Flexible explosive comprising rdx, hmx or petn and mixed plasticizer



United States Patent 3,400,025 FLEXIBLE EXPLOSIVE COMPRISING RDX, HMX 0R PETN AND MIXED PLASTICIZER John D. Hopper, Succasunna, and Franklin B. Wells,

Wharton, N.J., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Apr. 19, 1966, Ser. No. 545,790 14 Claims. (Cl. 149-48) ABSTRACT OF THE DISCLOSURE A flexible explosive of high power made essentially from a high explosive; a plasticizer which includes a liquid organic nitric acid ester, trimethylolethane trinitrate; and a high-viscosity nitrocellulose, and methods for making said flexible explosive.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to an explosive composition and more particularly concerns a flexible, self-supporting, water-resistant explosive and methods of making therefor.

Our composition comprises a particulate explosive employing a plasticized binder wherein the plasticizer for the binder contains a liquid organic nitric acid ester, the composition being useful in explosive metal-forming processes and admirably suited for demolition purposes. The composition is characterized further by safety in handling and may readily be formed into any desired shape as by rolling, extrusion, compression-molding, etc. into strips, blocks, sheets, and the like.

It is therefore an object of this invention to provide an explosive having the aforementioned characteristics.

Another object of this invention is to provide a flexible explosive of high power (up to at least 25% greater than that of TNT) and high brisance (rate of detonation up to at least 75,000 m./sec.) based on a finely divided explosive such as PETN, or preferably cyclotrimethylenetrinitramine (RDX) and/ or cyclotetramethylenetetranitramine (HMX).

Still another object of this invention is to provide an explosive which, in the form of sheets one-quarter inch or more thick, possesses suflicient flexibility so that it may be made to conform to the contour of uneven surfaces with a minimum of manipulation, thus aiding in the complete destruction of the device to be demolished.

A further object of this invention is to provide a flexible explosive having high resistance to impact and friction while retaining good cap-sensitivity characteristics.

A still further object of this invention is to provide a flexible explosive which is more heat-stable than similar materials currently available.

Yet another object of this invention is to provide a flexible explosive which is not adversely affected by water.

A final object of this invention is to provide an explosive of sufficient resilience so that when made in block or other massive form it will resist breaking up upon impact with a hard surface when striking such a surface with a velocity of at least 150 feet/ second.

Other and further objects of this invention will become apparent as the invention is further described hereinafter.

We have found that the foregoing objects may be attained through provisions of an explosive composition comprising about 4368% (preferably about 63%) of a particulate explosive such as PETN, RDX, HMX, or mixtures thereof, and having an average particle size of up to about 25 microns, preferably not over 13 microns. One hundred percent of the aforementioned particulate explosive must pass through a #200 U.S. Standard sieve,

Patented Sept. 3, 1968 and at least and preferably not less than 97.5% should pass through a #325 U.S. Standard sieve.

Our composition will also contain about 23.248.2%, preferably about 28.2%, of a plasticizer, one portion thereof being selected from the group consisting of tributyl acetylcitrate (preferred), dioctyl sebacate, triethylene glycol di (Z-ethylbutyrate), or other similar materials, preferably those having pour points of --40 C, or below, and being present to the extent of 4.226.2% of the total flexible explosive composition, and the other portion thereof being the liquid nitric acid ester trimethylolethane trinitrate (TMETN) to the extent of 240% of the total explosive composition, about 41 0%, preferably about 58% of a high-viscosity nitrocellulose binder containing about 12.1-12.S% nitrogen, of such a degree of polymerization as to have a viscosity, using a 4% solution of nitrocellulose and a 5/ l6-inch-diameter steel ball, of at least 90 seconds and preferably greater than seconds, as described hereinbelow, and about 00-10%, preferably about 03-08%, of a pigment to impart any desired color to the finished product.

In the determination of the nitrocellulose viscosity aforementioned, the steel ball shall weigh about 2.025 to 2.045 grams, the viscosimeter shall consist of a glass tube 14 inches in length with an internal diameter of 1 inch, immersed to the level of its liquid contents in a constant temperature bath maintained at 25:0.2 C., and the time of passage of the ball between markings shall be noted.

The aforementioned viscosity test is run in accordance with Specification MIL-N-244A, paragraphs 4.4.5 et seq., dated Feb. 13, 1962, with the exception that the quantities of materials used are: 8 grams nitrocellulose, 21.3 grams of ethyl alcohol, and 170.7 grams of acetone. The 21.3 gram/170.7-gram alcohol/acetone ratio is used to maintain the ratio required in the specification.

For purposes of camouflage, an olive-drab coloration of the explosive is most desirable. Less than 0.2% pigment is insufiicient to give a satisfactory coloration to the product where a color other than white is desired and the presence of more than 1% pigment is not necessary for effective coloring. The preferred pigment which imparts an olive-drab coloration to our explosive comprises one part lampblack and '8 parts lead chromate (chrome yellow, medium).

Liquid organic nitric acid esters other than TMETN which have been tried for possible use as plasticizers for nitrocellulose are glycerine trinitrate, glycol dinitrate, ethylene glycol dinitrate, 1,2,4-butanetriol trinitrate, triethylene glycol dinitrate, 1,2,6-hexanetriol trinitrate, and the like. Each of these esters presents a major drawback for its intended use, such as poor thermal stability, excessively high sensitivity, low explosive power, weak brisance, or tendency to cause the well known nitroglycerine headaches, and the like.

TMETN, upon contact with ordinary nitrocellulose, softens the outer layers thereof, but is incapable of colloiding the nitrocellulose normally used in the manufacture of single and double-base propellants. The highmolecular-weight nitrocellulose required for use in the present invention is even less affected by TMETN. We have discovered methods of colloiding the high-viscosity nitrocellulose in the presence of a high proportion of TMETN.

A series of tests has shown that the particulate explosive content of our explosive composition may be varied somewhat Without appreciably altering the properties of the resultant composition, except the rate of detonation, provided that the nitrocellulose total plasticizer ratio remains substantially within a 1:2.9 6 range and the inert ester (such as tributyl acetylcitrate) nitric acid ester ratio remains substantially within the coincident range of 4.2:24 to 26.2:2. However, while a composition containing 43% RDX, 8% nitrocellulose, 8.2% tributyl acetylcitrate, 40% TMETN, and 0.8% pigment had characteristics substantially identical with those of a composition containing 63% RDX, 8% nitrocellulose, 8.2% tributyl acetylcitrate, 20% TMETN, and 0.8% pigment, attempts to increase the RDX content above about 68% resulted in products which were somewhat stiff or which became rather hard after standing overnight.

In another series of tests it was found that the presence of about 0.4% added diphenylamine (DPA), a crystalline solid, improved the thermal stability of the explosive composition.

The products and processes of our invention are further described and illustrated by the examples hereinunder set forth.

EXAMPLE I The following materials were thoroughly blended about minutes in a sigma-blade mixer at l35i5 F.:

Grams Dry Type B, Class E RDX 1 315 Tributyl acetylcitrate 41 1 Specification MILR398C dated Aug. 22, 1962. The RDX used in this and subsequent examples contained 7.3% HMX unless otherwise noted.

Forty grams of nitrocellulose (96-second viscosity in 4% solution) was thoroughly wet with 40% ml. ethanol containing 2 grams DPA in solution. This alcohol-Wet DPA-treated nitrocellulose and 4 grams of the aforedescribed lampblack-chrome yellow pigment were added to the RDX-tributyl acetylcitrate mixture, the mixer closed, and the contents mixed about 30 minutes while maintaining the temperature in the mixer at l35i5 F. During mixing, about 50 ml. alcohol was added to obtain a heavy dough-like consistency in the mixture. After mixing, the mix was placed in a covered container and let age overnight. In the preparation of other identical mixes, it was found that the addition of about 50 ml. of a nitrocellulose solvent, such as ethyl acetate, to the mixture which is to be aged, prior to TMETN addition, shortens the aging period and aids in the subsequent incorporation of the TMETN into the mix. The aged mix was then returned to the mixer, which was held at 135:5 F., 100 grams TMETN added, and the whole blended 30 minutes with the mixer open. The mix was then rolled on polished steel rolls held at 135":5 F., first with a roll gap of 0.010 inch to assure evaporation of volatile, and then at a setting of about 0.2300.240 inch to consolidate the material into a substantially inch thick sheet which was smooth and uniform in appearance. During the preparation of additional identical mixes, it was found that the first rolling at a setting of 0.010 inch may be advantageously carried out at a temperature of 150;L-5" F., that below 130 F. volatiles evaporation is undesirably slow, and that consolidation into sheets about inch thick is most advantageously carried out at about 125 130 F., although both higher and lower temperatures may be used. It was found, also, that the flexible explosive this prepared was well-suited for formation of desired shapes by extrusion. Perfect filaments as small as 4; inch in diameter were prepared by extrusion at about 135 F. Test values obtained with this material were:

d 1.539 Vacuum stability (5 g./40 hrs/100 C.)

ml. gas 1.09 Ballistic Mortar Test Value (TNT value=1.00) 1.25 Picatinny Arsenal Impact Sensitivity Test inches 16 Picatinny Arsenal Explosion Temperature Test C. smoke 258 Friction Pendulum Test (w./ steel shoe) No action Rate of detonation m./sec 7441 The symbol (1 indicates the ratio of the density of the material at 20 C. to the density of water at 4 C.

The Friction Pendulum Test and Ballistic Motar Test are described in Picatinny Arsenal Testing Manual, May 8, 1950, J. H. McIvor, in Manual 71 and 72 respectively.

The Picatinny Arsenal Impact Sensitivity Test and Explosion Temperature Test are described in Standard Laboratory Procedures for Sensitivity, Brisance, and Stability of Explosives, PTTR No. 1401, Mar. 18, 1944, Revised Feb. 28, 1950, W. R. Rinkenbach and A. J. Clear.

EXAMPLE II The composition of this example varied from that of Example I only in that 6.2% of tributyl acetylcitrate and 22% of TMETN, rather than 8.2% and 20% respectively, were used. Also, 140-second viscosity (in 4% solution) nitrocellulose was used, and 50 ml. ethyl acetate was added to the mix before aging prior to TMETN addition. This mix produced a sheet which was smooth and uniform in appearance. Test values obtained with this material were:

d 1.545 Rate of detonation m./sec 7515 Vacuum stability (5 g./40 hrs/100 C.)

ml. gas 1.42 Ballistic Motar Test Value (TNT value=1.00) 1.27 Flexibility Test (Passed) F 0 Picatinny Arsenal Impact Sensitivity Test inches 10 Picatinny Arsenal Explosion Temperature Test C. smoke 262 Cap sensitivity cap No 8 The Flexibility Test comprises bending the explosive sample around a A inch diameter mandrel in 5 seconds at 0 F. The sample broke when tested at l0 F but at 0 F. it neither broke nor cracked.

The Vacuum Stability Test at C. is described in specification Standard MIL-ST D-650, Method 503.1.

Samples prepared with P ETN, with HMX, and with RDX containing 2.5% HMX gave products substantially similar to that noted above.

EXAMPLE III The composition of this example varied from that of Example I in that no DPA was present and 4.2% of tributyl acetylcitrate and 24% of TMETN were used. This mix produced a sheet which was smooth and uniform in appearance but was somewhat stiflfer than the sheets obtained from the mixes of the preceding examples.

Compositions containing 63% RDX 'but with decreasing amounts of substitution of TMETN for tributyl acetylcitrate gave smooth uniform sheets which, as the TMETN content dropped toward 0%, showed a substantially uniform density decrease to a value of about 1.470, a rate of detonation decrease to about 7000 m./sec., and a decrease in ballistic mortar test value to about 1.0. Compositions containing small amounts of TMETN could be worked up into smooth uniform sheets without aging or addition of ethyl acetate or other nitrocellulose solvent.

EXAMPLE IV The composition of this example varied from that of Example I only in that 20.2% of tributyl acetylcitrate and 6.0% TMETN were used. This mix produced a sheet having a smooth uniform appearance.

(1 1.5 Rate of detonation m./sec 7186 EXAMPLE V The composition of this example varied from that of Example I only in that 26.2% tributyl acetylcitrate and 1 1.47 Rate of detonation m./sec 7008 EXAMPLE VI EXAMPLE VII The flexible explosive of this example was identical in composition to Example I. This material was extruded in one-quarter-inch thick strips having an average density of 1.6140 g./cc. It was also extruded in 2-inch x 4-inch bars whose average density was 1.6081 g./cc. Another identical mix was extruded in one-quarter-inch thick strips which had an average density of 1.6197 g./cc.; onequarter-inch thick sheets obtained by rolling had an average density of 1.5450 g./cc.

EXAMPLE VIII The composition of this example varied from that of Example VII only in that 112-second viscosity (in 4% solution) nitrocellulose was used in HMX 1 was substituted for RIDX. This material was rolled to give a smooth, uniform, one-quarter-inch thick sheet. Test values obtained with this material were:

d 1.6036 Vacuum stability (5 g./ 40 hrs./ 100 C.) ml. gas 1.26 Picatinny Arsenal Impact Sensitivity Test in ches 1 1 Picatinny Arsenal Explosion Temperature Test, smoke C 262 Rate of detonation m./sec 7549 Cap sensitivity cap 1 M6 111 accordance With Specification MILC4546SA(MU) dated May 15, 1964.

EXAMPLE D( The composition of this example varied from that of Example VIII only in that the particulate high explosive used consisted of a mixture containing equal proportions of RDX and HMX so that there was 31.5% of each in the finished flexible explosive, which was rolled into a smooth uniform one-quarter-inch thick sheet. Test results obtained with this material were:

r1 1.5697 Vacuum stability (5 g./40 hrs./ 100 C.) ml. gas 1.23 Picatinny Arsenal Impact Sensitivity Test inches 13 Picatinny Arsenal Explosion Temperature Test, smoke C 246 Rate of detonation m./sec 7407 Cap sensitivity cap No 8 EXAMPLE X The composition of this example varied from that of Example VII only in that the particulate high explosive used consisted entirely of fine PETN. This composition Grade II, Class B HMX as specified in Specification MIL-H45444A(Ord). Amendment 3 dated July 31, 1962.

The HMX used in this and the following example contained 1.55% RDX.

was rolled into a smooth, uniform, one-quarter-inch thick sheet. Test values obtained with this material were:

d 1.4863 Vacuum stability (5 g./40 hrs./ C.) .1111. gas 1.55 Picatinny Arsenal Impact Sensitivity Test inches 9 Picatinny Arsenal Explosion Temperature Test, flame C 235 Rate of detonation m./sec 7274 Cap sensitivity cap No 5 While the present invention has been described in detail, it will be apparent to those skilled in the art that there are many variations possible without departing from the scope of this invention, which is limited only by the appended claims.

We claim: 1. A self-supporting, resilient, high-powered, brisant, flexible explosive composition of good cap-sensitiveness, low impact-sensitiveness, good heat stability and water resistance including a particulate explosive selected from the group consisting of cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), and pentaerythritol tetranitrate (PETN), said flexible explosive composition comprising; about 4368 weight percent of at least one member selected from the group consisting of RDX, HMX, and PETN, about 23.2-48.2 weight percent of a mixed plasticizer including a first portion and a second portion, said second portion being a liquid organic nitric acid ester trimethylolethane trinitrate, said second portion of said plasticizer comprising about 2-40 weight percent of total flexible explosive composition, and about 4-10 weight percent of a high viscosity nitrocellulose.

2. The composition of claim 1 further characterized by said particulate explosive having an average particle size of up to about 25 microns.

3. The composition of claim 1 wherein said first portion of the mixed plasticizer is selected from the group consisting of tributyl acetylcitrate, dioctyl sebacate, and triethylene glycol di (Z-ethylbutyrate), said first portion of the plasticizer having a pour point not exceeding about 40 C. and comprising about 4.226.2% of the total flexible explosive composition.

4. The composition of claim 1 wherein 100.4 parts thereof contain 0.4 part of a diphenylamine stabilizer. 5. The composition of claim 1 including about 0.2 to 1.0 weight percent of a pigment consisting essentially of one part lampblack and 8 parts chrome yellow medium.

6. The composition of claim 1 wherein said high viscosity nitrocellulose contains preferably about 12.1 to 12.5 weight percent nitrogen.

7. A method for the preparation of a flexible, highpowered explosive composition of good cap-sensitiveness, low impact-sensitiveness, good heat stability and water resistance comprising the steps of blending about 63 parts by weight of a particulate high explosive selected from the group consisting of RDX, HMX, PETN, and mixtures thereof and about 8.2 parts by weight of tributyl acetylcitrate in a mixer at elevated temperatures to form a first mixture,

wetting about 8 parts by weight of a high viscosity nitrocellulose with about 8 parts by volume of ethanol containing 0.4 part by weight of diphenylamine stabilizer in solution to form a second mixture,

thoroughly mixing said first mixture and said second mixture at elevated temperatures while adding thereto about 10 parts by volume of ethanol to form a resultant mixture,

removing said resultant mixture from said mixer,

aging said resultant mixture,

blending said resultant mixture with 20 parts by weight of trimethylolethane trinitrate at elevated temperatures to form a final mixture and forming said final mixture into a desired shape.

8. A method according to claim 7 wherein said forming step comprises extruding.

9. The method of claim 7 further characterized by mixing about 0.8 part by weight of pigment comprising about one part lampblack and about 8 parts lead chromate to said second mixture.

10. The method of claim 7 further characterized by said first mixture containing about 42-262 parts by weight of tributyl acetylcitrate and said resultant mixture is blended with about 240 parts by weight of trimethylolethane trinitrate such that the total amount of tributyl acetylcitrate and trimethylolethane trinitrate totals about 23-482 parts by weight.

11. The method of claim 10 further characterized by mixing about 0.8 part by weight of pigment comprising about one part lampblack and about 8 parts lead chromate to said first and said second mixture.

12. A method according to claim 7 wherein said explosive comprises RDX, about 10 parts by volume ethyl acetate is incorporated into said resultant mixture, and said forming step comprises rolling.

References Cited UNITED STATES PATENTS 2,768,072 10/1956 Stark 149 92x 2,852,359 9/1958 Achilles 149-95 X 2,916,996 12/1959 Coffee 149 93 x LELAND A. SEBASTIAN, Primary Examiner.

CARL D. QUARFORTH, Examiner. 

